Security documents having thermoplastic substrates, such as identification cards, licenses, government service cards, passport pages and others and the web sheets they are cut from, normally include one or more printed personalization images (e.g. a printed photograph of a cardholder) used to identify the cardholder or otherwise authenticate the security document which may be printed onto a surface of the substrate using inkjet printing, for example, using an ink which may be single or multi-coloured and/or ultraviolet (UV) curable.
Prior to the invention of the subject matter of the Applicant's co-pending U.S. application Ser. No. 13/381,666 filed on 28 Dec. 2011 (published on 4 July, 2013 under publication no. 2013/0171423), the content of which is incorporated by reference, such images were printed onto a smooth or matte surface of the thermoplastic substrate of the card. Optionally, a clear protective coating was applied over it, or a patch was glued over it, to try to improve the durability of the printed image. However, both the printed image and any protective coating or glued patch (often referred to as a hot laminate patch) applied to such smooth or matte surface does not durably adhere to such a surface so their attachment is inherently weak. Such coatings and patches are prone to detach and, thus, they are unable to effectively protect the printed image. Optimally, such printed images would be protected by embedding them between layers of the card substrate. However, prior to the present invention this could not be achieved because the ink of the print image prevents a similar thermoplastic layer from bonding to it. Instead, only a relatively weak adherence occurs between the surfaces of a printed thermoplastic layer and another thermoplastic layer applied over the printed layer.
The Applicant previously invented a method of printing a durable image on a thermoplastic substrate by preconfiguring the surface of the thermoplastic substrate to have a pattern of recessed image receiving surfaces below a nominal surface of the substrate, as described in said co-pending U.S. application Ser. No. 13/381,666. Advantageously, the recessed surface areas in which the image is printed serve to increase the durability of the printed image as compared to printing the image on the normal (smooth or matte) surface of a thermoplastic substrate. However, that invention, while improving the durability of an image applied to a thermoplastic substrate did not contemplate or address any need or desirability to provide further protection to an image printed in accordance with that invention.